The present invention relates to a mobile communication system and more particularly to an efficient data packet service for a Code Division Multiple Access (CDMA) mobile communication system of the next generation.
A mobile communication system generally includes a plurality of base stations which coordinate a wireless communication among users of mobile stations at various locations. Each base station provides communication service to mobile stations within the base station""s coverage area by receiving data packets from a mobile station and directing the data packet to a mobile switching center. Particularly, the data packets are transmitted through a specific frequency bandwidth allocated to one of the base station. The amount of data packets that can be simultaneously transmitted is limited by the frequency bandwidth. Thus, one mobile station has a capacity to provide communication service to a fixed number of mobile stations. Currently, the CDMA mobile communication system lacks a way to control the traffic load of a frequency bandwidth allocated to one mobile station when the amount of communication service requested surpasses the capacity of the mobile station.
In the CDMA mobile communication system of the next generation, the states of the mobile station and the base station/base station controller (BS/BSC) is managed by a predefined Medium Access Control Sub-Layer (MAC). Generally, the mobile station and the BS/BSC may exist in an Active State, a Control State, a Suspended State, or a Dormant State. Under the management of the MAC, the states of the mobile station and BS/BSC are static. Thus, if a large number of mobile stations is receiving data packet service from the same base station, the large number of mobile station exchange data frames with the base station in an activated state of the base station.
Accordingly, a base station which is providing only voice packet service would be in an inactivated state for a very brief period, thereby maintaining a constant load on the communication system. Moreover, the base station must reject new service requests from mobile stations due to a high frame error rate (FER). However, from the standpoint of a mobile station user already receiving a data packet service, the base station would be in a dormant state even though the service has not been completed. Thus, if the user has more data to send, the user would send a new service request reactivating the base station which may overload the communication system depending on the requested service.
FIGS. 1(a) and (b) show the state transition of a BS/BSC and a mobile station during a data packet service in the related art. If a data frame being transmitted in the forward direction from the BS/BSC to a mobile station does not exist for a predetermined time period (Tactive), a message is sent to the mobile station requesting a state transition. The mobile station receives the message and sends a reply message (ACK) after a state transition. Likewise, if a data frame being transmitted in the reverse direction from the mobile station to the BS/BSC does not exist for a predetermined time period Tactive, a message is sent to the BS/BSC requesting a state transition. The BS/BSC receives the message and sends a reply message ACK after a state transition.
In order to make a transition from one state to another, a mobile station or BS/BSC activates a timer with a predetermined time period. When the predetermined time period has elapsed, a message requesting a state transition is sent in the forward and the reverse direction (S1, S3). The transition of states is managed between the MAC of the mobile station and the MAC of the BS/BSC.
Particularly, a mobile station receiving a data packet service remains in the Active State during the time period of sending the data. However, a timer with a predetermined time period has been activated to send a message requesting a state transition to the Control State. Thus, if there are no data transmitted between the mobile station and the BS/BSC for the predetermined time period, a message requesting a state transition is sent in the forward and the reverse directions (S1, S3). Upon receiving the state transition request and after a state transition to the Control State, a reply message ACK is sent back in the reverse and the forward directions (S2, S4).
If a mobile station in the Control State receives a new request for data transmission from a user, the states reverts back to the Active State. However, if there is no request for data service for another predetermined time period of the timer, the state of the mobile station changes to the Suspended State. The state transition is executed in the same manner as before by activating a timer and sending messages requesting a state transition (S1, S3). If the mobile station in the Suspended State determines that there is no more data to be transmitted, the state of the mobile station changes to the Dormant State according to the lapsed time period of the activated timer.
The CDMA mobile communication of the next generation described thus far provides data packet service by managing the state transitions of all the mobile stations receiving the data packet service according to the timer. Using the timer, the logical channels and the physical channels are assigned to and withdrawn from the mobile stations. Accordingly, when the data service request level surpasses the capacity load of a base station, the communication system cannot dynamically manage the mobile stations receiving data packet service.
Generally, the transmission of data packets may be delayed without affecting the quality of the communication service. In contrast, if the transmission of voice packets is delayed, the transmitted message may create long periods of pauses or a stuttering effect at the user side of the mobile station receiving the voice packets, especially for a real-time phone conversation. Despite the different susceptibilities to a delay in transmission time, the mobile communication system in the related art does not distinguish between a voice packet service and a data packet service.
For example, during a period of a heavy traffic load, the mobile communication system does not have a system of an Automatic Repeat Request for a voice packet service. Also, if a base station provides data packet service to mobile stations at a full capacity, the FER of the data packets already being transmitted would more likely increase. Thus, the mobile communication system cannot ensure the quality of the data packet service provided to the mobile stations receiving the service.
Since the transmission of data packets are less susceptible to delays, the quality of the data packet service may be improved through the Radio Link Protocol (RLP) by requesting for a re-transmission of the data frames having an error. However, numerous requests for re-transmission of data frames would further burden the traffic load, especially if the base station is already functioning near full capacity. In such situations, a user at the mobile station may not be able receive the data frames requested by a re-transmission. Furthermore, during an actual packet data service, a Transmission Control Protocol (TCP) frame is transmitted in segments. If one segment of the frame has not been received, the TCP frame as a whole is considered invalid and a request is made for a re-transmission of all the segments of the frame.
Eventually, the number of requests for data packet service will increase resulting in a heavier traffic load for a base station to transmit the data packets. Without an adequate solution to manage the traffic load, a mobile station cannot easily make a transition from one of the inactive states to the Active State. Even if a mobile station successfully makes a transition to the Active State and requests a data packet service, the user of the mobile station is less likely to receive a satisfactory service due to a heavy traffic load. Similarly, a user of a mobile station already receiving voice packet service would less likely receive a satisfactory service due to the increasing traffic load.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
An object of the present invention is to provide mobile communication with a capacity of one base station to serve a greater number of mobile stations.
Another object of the present invention is to provide a mobile communication with a high quality of service for both data and voice packets, even when the traffic load is heavy.
A further object of the present invention is to provide a mobile communication with a dynamic management of the state transitions.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.